Hydrogen cyanide is obtained in a large number of industrial processes either directly or accumulates as a byproduct.
Thus one begins with the customary industrial process for the production of hydrogen cyanide from hydrocarbons and ammonia with or without the presence of oxygen, or obtains hydrocyanic acid, e.g. as byproduct in the so-called Sohio synthesis for the recovery of acrylonitrile (Ullmann, Enzyklopadie der technischen Chemie, Vol. 9, 4th Edition, pages 657 et seq.).
Also coke plant, refinery and furnace gases contain hydrogen cyanide in various amounts, see Ullmann, loc. cit.
In all processes for production there are obtained hydrogen cyanide containing waste gases, as is also true with coke plant, refinery and furnace gases, which contain so little hydrogen cyanide that their working up to hydrogen cyanide or hydrogen cyanide containing compounds does not pay.
In all of these cases previously it was much commoner for separation or rendering non-toxic the hydrocyanic acid containing gases to use absorption, adsorption or thermal processes. (Winnacker-Kuchler, Vol. 7 (1975) pages 693 et seg.).
However, in the absorption methods the hydrocyanic acid is converted thereby into cyanide compounds which usually requires an expensive decontamination since a further use is seldom possible because of their low purity. Also there is always the danger of a spontaneous polymerization in the presence of alkalies.
Adsorptive processes, e.g. with activated carbon, aluminum oxide or molecular sieves, indeed have the advantages that they are capable of regeneration, however, they assume that the gases added do not contain suspended matter; however, additionally the polymerization of hydrocyanic acid occurs preferably on large surface areas so that the adsorption towers can be clogged after a short time.
Industrial processes, as e.g. the freezing of hydrocyanic acid from the gases are only meaningful industrially with sufficiently high concentrations of hydrocyanic acid.
A flame combustion in torches or a catalytic combustion, e.g. in the presence of metal oxides, see German OS 2531720, indeed permits accomplishment of the result with simple means but besides the total loss of hydrocyanic acid usually leads to a high loading of the environment.
The change of hydrogen cyanide to ammonia through hydrolysis in aqueous medium or through reductive splitting is known as of itself (Gmelin, N-Vol. 4, page 365).
Thus, e.g there is used the hydrolysis of the hydrogen cyanide in the Kjeldahl method for determination of total nitrogen.
However, this method is not suited for the industrial transformation of hydrogen cyanide containing gases into ammonia containing gases.
Indeed it is also known according to Beilstein's Handbuch der Organischen Chemie, Vol. II, 1920, 4th Edition, page 36 to obtain ammonia through reduction of hydrogen cyanide with hydrogen in the presence of nickel above 250.degree. C., but only as a component of a mixture with the methyl amines.
Likewise the non-catalytic process described in German Pat. No. 232,878 in which hydrogen cyanide containing gases are reacted at at least 1000.degree. C. with steam to form ammonia, only represents an illustration of the hydrolysis process.
It was the problem of the present invention to develop a process for changing hydrogen cyanide containing gases into valuable materials.